Spray metal coated, metal surfaced articles



Patented May 25, 1943 SPRAY METAL COATED, METAL SURFACE!) ARTICLES JohnFrank Meduna, Seattle, Wash, assignor to Metallizing Engineering (70.,Ind, Long Island City, N. Y., a corporation of New Jersey No Drawing.Application August 6, 1942, Serial No. 453,905

8 mamas. (01. 117-71) This invention relates to new anduseful'improvements in spray metal coated, metal-surfaced articles.

In industrial practice, a coating of metal is frequently applied to abase of the sameor other metal by spraying. For this purpose, the metalto be applied is projected against the surface to be covered in the formof a spray, the particles of which are in a molten or heat plasticcondition. As a rule, metal spraying is carried out with the use ofmetal spray guns, i. e., devices in which the metal is fed to a heatingzone from which zone metalparticles, at least some of which are moltenor in a heat plastic condition, are propelled against the surface to besprayed, by a blast of air or other gas. The application of sprayedmetal may, for example, be carried out to profeet the base againstcorrosion, to provide a surfac of the desired ornamental or bearingcharacteristics, or to build up worn machine parts.

In making spray metal coated articles, particularly re-built hearings orother working surfacesof machine parts, it is essential that the appliedspray metal adheres to the surface to which it is applied with a highdegree of bond, for, otherwise the applied spray metal will come off. Inthe past, spray metal coated, metal-surfaced articles have beengenerally of two kinds. Those in which the base is pre-conditioned forspray metal bonding by mechanical roughening and those in which the base.is so pre-conditioned by heating.

Mechanical roughening of a metal surface to adapt the same to receiveand retain applied spray metal must be of-a type involving the formationof a multiple number of closely spaced cavities with peened and splayededges and interspaces, forming a multitude of lreyways. Hitherto, the

' most common method of procuring such type surcome apart by reason ofthe deficient bond obtaining between the spray metal coating and theblasted surface. This is particularly true when heavier spray metalcoatings have been applied to substantially fiat surfaces and in caseswhere spray metal has been applied to surfaces forming an insidediameter. Spray metal has a tendency to shrink and in these cases thesander grit blasted surface does not provide a sumcient bonding surfaceto prevent the separation of the applied spz'ay metal coating fromlthebase. For this reason. for instance. it has never been practical to makespray metal coated, hardened engine valve seats or similar objects inwhich an especially strong bond between the spray metal coating and thebase is required. Furthermore, many bases and particularly thoseconstitutedbymachine tools or parts such as, for instance, generatorshafts or the like, are inherently unsuitable for sand or grit blasting.

An alternative form. of mechanical surface roughening for spray metalbonding purposes is that of machine roughening the surface to be sprayedin a particular manner designed to procure the above-mentioned surfacecharacteristics essential for spray metal bonding. The articles obtainedby this roughening method, however, are subject to substantially thesame inherent limitations and drawbacks as those prepared from a sand orgrit blasted base.

The heating method of surface conditioning a metallic base to bondthereto applied spray metal involves the heating of the surface to arela tively high temperature and to spray the hot surface with metal.This method is not widely used and requires, as a general rule,considerable skill and elaborate equipment and is relatively expensive.Furthermore, in most cases the temperature to which the surface or basemust be heated is so high that it tends to warp or otherwise destroy thearticle to which the metal spray is to be applied. Hence, it is in manycases impossible to obtain satisfactory spray metal coated articleshaving the spray metal directly heat bonded to its base.

There is one basic limitation inherent in practically all of thehitherto used spray metal bonding means. 'This limitation resides in thefact that these bonding means are not adaptable to harden metal articlesor surfaces. Many hardened articles or surfaces cannot be properlysurface-conditioned by mechanical roughening procedures such as grit orsand blasting or roughmachining. On the other hand, the heatin method isnot feasible, for most such metal articles 6r surfaces will soften andthus lose their hardness if they are heated to the temperature necessaryto secure the desired degree of bondin to the spray metal appliedthereto. Though partly hardened articles have been prepared by grit orsand blasting, using very hard grit such as aluminum oxide abrasives,nevertheless, the bond obtained is usually unsatisfactory.

One object of the invention comprises inter alia a spray metal coated,metal-surfaced article substantially free from the limitations anddrawbacks characterizing hitherto knownspray metal coated,metal-surfaced articles. objects of the invention will be apparent fromthe following description.

The spray metal coated, metal-surfaced article in accordance with theinvention essentially comprises an article having a metal surface, alayer of spray metal, and, intermediate said metal surface and saidlayer of spray metal, metal deposited upon and bonded to said surface byfusion and characterized by an irregular surface frozen This and furtherfrom semi-liquid state with a multitude of projections with overhangingedges and minute craters with overhanging edges, at least the majorityof said projections and craters being in interlock with spray metalparticles of said layer of spray metal.

I have found that best results and a particularly good interlock withthe super imposed spray metal are obtained by so selecting the size andspacing of the projections and'craters on the surface of thefusion-deposited metal that the same are of substantially the same orderof magnitude as the size of spray metal particles in the spray metallayer.

Within the preferred embodiment of the invention the irregular surfaceof fusion-deposited metal is preferably so constituted as to have inaddition to the projections of the order of magnitude of spray metalparticles, projections of a higher order of magnitude and preferably ofan order of magnitude not appreciably in excess of 116'! nitude, thoughnot necessarily acting as interlocks with spray metal particles of thesuperimposed layer of spray metal, nevertheless, contribute to the bondby counter acting or preventing slippage of the spray metal layer withrespect to the base surface, resulting from the shrinkage of the appliedspray metal.

One method, inter alia, of preparing a spray metal coated article inaccordance with the invention may be for instance by the deposition ofelectrode material upon the metal surface of such article and thesubsequent application of spray metal to the thusly treated base. Theprocedure of depositing electrode material broadly involves establishingcontact between such metal surface and a metal electrode, electricallyheating the contacting surfaces .of the electrode and the metal surfaceby means of an electric current flowing through said contacting surfacesunder conditions of resistance heating to substantially fuse electrodematerial and firmly bond the same to said metal surface and causingsmall amounts of electrode material to be left deposited on the metalsurface. By such fusion-deposition of electrode metal the latter isbonded by fusion to the base leaving a surface of the desired irregularprojection and crater pattern without the necessity of furthertreatment. at least some of the metal deposits relatively large, aidedif necessary by increases in amperage, the resulting irregular patternedsurface will include the larger type projections above referred to.

The electrode material that may be used is preferably of the wire type,i. e., of the type in which a wire or bar, whether round," flat or ofany other shape, constitutes an electrode. For best results, a nickelwire electrode is preferred. A commercial nickel wire constitutes asatisfactory wire electrode. It is understood that electrode size andelectric current should be suitably coordinated.

Contact between the metal electrode and the metal surface to beconditioned for the metal spraying operation is established in theordinary manner by placing the electrode in direct contact with suchsurface. Within the range of normal requirements, practically any metalsurface and any metal electrode may be used. In case, however, anyparticular electrode metal should prove unsuitable or unsatisfactory inits application to a given metal surface of a base to be conditioned forspraying, the operator can de- These projections of higher order of mag-When making termine by a few simple empirical tests as to whichelectrode metal to select. As a practical guide any two metals that canbe joined by heating will operate as electrode material on the surfaceto be conditioned for spraying.

The electric heating of the contacting surfaces of the metal electrodeand metal surface to be conditioned for spraying may be effected byplacing the electrode and the metal surface in electric circuit with asource of electrical energy in such manner that the circuitis closed bycontact between the metal surface and the metal electrode. Theconditions of current flow in the circuit upon so closing the sameare'preferably so adjusted that conditions of resistance heating at thecontacting surfaces of electrode and metal surface maintain. Byconditions of resistance heating I mean that the current flowing throughthe contacting surfaces is in amount. and intensity sufficient to causeheating at the contacting surfaces by the resistance offered the freeflow of the current by reason of the joint constituted by the contactingsurfaces.

Though voltages having a wide range, including relatively high voltagesof the order of magnitudeof one hundred or two hundred volts or more,may be used, I prefer to use voltages of a lower order of magnitude. Oneof the reasons for the preference for a lower voltage range is thathigher voltages have a tendency to are badly particularly when makingand breaking contact between the electrode and the metal surface,whether the making and breaking be deliberately induced or caused by theunevenness of the surface treated. Though relatively mild arcing may. bebeneficial in the procurement of a satisfac torily conditioned surface,excessive arcing is under normal conditions an undesirable aspect,impairing satisfactory deposit of electrode material. Considerableamounts of metal may be lost as the result of the high temperaturescaused by the are thereby tending to render the procedure lessefficient. Furthermore, such arcing is attended by operationaldifliculties which would often require a greater skill on the part ofthe operator and or suitable control mechanism. A still furtherdisadvantage of excessive arcing is the formation of metal oxide whichmay tend to impair the bond in certain cases between the conditionedsurface and thereto applied spray metal. It is best, therefore, to soadjust the conditions of current flow in the circuit that, upon closingor breaking the same, the current intensity is sufficiently low to avoidexcessive arcing and yet have the current in amount and intensitysufficient to cause the desired deposition and bonding of electrodematerial.

While very low voltages such as even fractions of one volt can be usedand give, when applied with care, fairly satisfactory results, such lowvoltages are as a rule not desirable for largescale eificient operationsas they require the use of relatively small .or at least fairly sharppointed electrodes so that the procedure is slow.

In general, a satisfactory current will depend upon the voltage, thesize of the electrodes and principally upon the amount of contactbetween the electrode and the metal surface of thebase to be sprayed.These factors may be adjusted to suit particular conditions. Averagevoltages from one-half to twenty voltsgive satisfactory results. Forbest results, however, a voltage range of from two to nine volts isordinarily to be preferred. The amount of current to be used may varyover a wide range depending upon the accuses factors hereinaboverecited. As a general rule, when using wire electrodes a current inexcess of two hundred amperes and mostpreferably a current of the orderof magnitude of about 300 to 400 amperes is satisfactory. Thus, forinstance, a 300 ampere current gives good results with aA a" nickel wireelectrode. When using larger electrodes the use of larger amounts ofcurrent may be necessary.

The deposition of small amounts of electrode material may be causedeither by the melting off of small amounts of electrode material fromthe tip of the electrode or by pulling ofi small amounts of fusedsurface bonded electrode material from the tip of the electrode whenmoving the latter. In the majority of cases, deposition of electrodematerial may becaused in both of these manners. Moving of the electrodewill as a rule, accomplish the desired deposition of small amounts ofelectrode material firmly bonded to the surface area to which electrodecontact was applied.

The metal surface to be conditioned for spray metal application wheninserted in circuit, as

' above set forth, with a suitable metal electrode sometimes advisableto move the electrode relative the base while maintainingresistance-heating contact therebetween. When proceeding in this manner,electrode material is deposited in ridges along the path of movement ofthe electrode relative the metal base. On the other hand, in the makingand breaking contact method small amounts of individual electrodematerial are deposited upon the metal base. The pro-- cedure iscontinued or repeated. in either case until the surface to be sprayed issatisfactorily covered with electrode material. taken that the electrodeis not left in a contact position too long at any one point or area asthis may cause the permanent attachment of the electrode to the base andthus render its further movement and further deposit of electrodematerial impossible.

It is not necessary to have every spot on the metal base covered by thefusion-deposited metal; on the contrary it is-sufiicient to deposit alarge number of small, closely spaced, amounts Care should be lib ofmetal with spaces in between some of them. I

The size of the spaces between deposited amounts of metal may be variedover a reasonably wide range at the judgment of the operator. Broadlystated, the smaller the spaces the stronger a bond will result andtherefore where a strong bond is not desired the deposits may be quitewidely spaced. For a strong bond, however, it is preferred to havespaces between amounts of fusion-deposited metal not appreciably inexcess of Eh!!! The amount of metal, fusion-deposited on the base, aswell as the size of the larger type fr regular projections, if such arepresent, may be varied to suit conditions or requirements. When a heavyspray metal coating is tobe deposited, it is advisable to make some ofthe larger type projections relatively large. Some of these proiectionsmay thus, for instance, extend as much as or even more. However, where athin coating such as a coating is to be applied by metal spraying, theheight of these larger type projections is preferably kept at less thanthe thickness of the spray metal coating to be applied, i. e., less thanas otherwise. if the spray metal coating is machined smooth, theseprojections will extend through the coating to the machined surface.There are, however, some applications where this is no disadvantage.

It is sometimes advantageous to make the larger type projectionsrelatively so high that they will extend to beyond the thickness of thecoating of sprayed metal that is to be applied, and then. machine off ortool ofl their tops, so that they will not project through the spraymetal coating to be applied. Thereafter, the spray metal coat may beapplied.

If desired, small amounts of metal may be fusion-deposited, as describedpreviously, to the base and then the deposition continued so that moremetal is so deposited on top of metal previously deposited, as well asin the spaces between previously fusion-deposited metal, a relativelythick metal may be applied. Within normal requirements, the thickness ofthe coating of intermediate-layer metal has, in itself, as a rule, noeffect upon the bond with which the subsequently applied spray metal isheld thereto and thus to the base surface of the spray metal coatedarticle in accordance with the invention.

The intermediate layer metal may be deposited upon a suitable metalbase, in any one of a number of patterns. For instance, the metal may bedeposited, although in small successive amounts, in strips or ridges, orit may be deposited in separate isolated spots, or, for'instance, incrisscross pattern. l

The following examples are furnished by way of illustrating proceduresfor procuring my novel spray metal-coated metal-surfaced articles:

Example I A source of electric energy consisting of a transformerconnected to an alternating current power supply is first provided,capable of an average voltage between two and nine volts andapproximately 300 amperes. One lead from the source of electric energyis connected to a 2 x 3 x /4" steel plate, the top surface of which isto eceive fusion-deposited metal and has been suita ly cleaned such asby application ,pf CCM to remove grease and dirt. The other lead fromthe source of electrical energy is connected to a nickel wire ofapproximately diameter. The nickel wire is first contacted with the topsurface of the steel plate and as soon as the metal of the electrodestarts to melt the contacted surface is lightly and continuously strokedwith the make and break contactrepetitiously with sucthe treatment isdiscontinued and the surface is' then' sprayed in the conventionalmanner with bronze. i

Emample l! A source of electrical energy consisting of a direct currentgenerator is first provided, capable of producing a voltage of 5 voltsand approxiapproximately 1 3" mately 400 amperes. One lead from thesource of electrical energy is connected to a bronze sleeve, thepreviously cleaned outside surface of which is to receivefusion-deposited metal; the other lead from the source of electricalenergy is connected to a stainless steel strip of flat wire thick by A"wide. The stainless steel strip is first contacted with the surface ofthe bronze sleeve, preferably on the edge of the strip, and as soon asthe metal of the strip electrode starts to melt the contacted surface islightly and intermittently stroked with the stainless steel strip oversuccessive areas of the same whereby the end of the stainless steelstrip is caused to make and break contact repetitiously with successiveportions of the surface. After the desired surface of the sleeve hasbeen substantially covered by a large number of relatively closelyspaced amounts of fusion-deposited stainless steel from the stripelectrode, the treatment is discontinued and the surface is then sprayedwith aluminum.

Thus the article produced in accordance with the foregoing Example Iconstitutes a composite metal article comprising a steel base, a layerof spray bronze, and intermediate the steel base and the layer of spraybronze, nickel deposited by fusion on the steel base in interlock'withthe spray bronze by means of the specifically peculiar multitude ofminute surface craters a d overhanging characteristics of the fusion-doeposited metal. The article obtained in accordance with Example IIconstitutes a similar composite metal article except that in this casethe base is of bronze, the fusion-deposited metal, stainless steel andthe' therewith interlockin spray metal layer, sprayed aluminum.

When in the preparation of the products in accordance with my invention,a base of substantially cylindrical configuration is used. as, forinstance, constituted by shafts, sleeves, rods, bars and the like, it isoften of advantage to apply the fusion-deposited metal by rotating theobject about its axis and proceeding with the hereinabove electrodecontact procedure while the object is rotating. In such case, electrodecontact if desired may be substantially continuous though it ispreferred to use the repetitious contact stroking method'above referredto. R- tation of the cylindrical shaped base may be accomplished in anydesired manner, it being preferred, however, to rotatably mount the samein a suitable lathe or such similar machine. Surface speed of rotationshould not be appreciably in excess of 200 feet per minute, andpreferably substantially between 50 and 150 feet per minute. When usingsurface speed appreciably in excess of 200 feet per minute, considerablevoltage drops result by reason of reduced contact; furthermore, thespacing of deposited metal becomes too large and overlaps occur, therebyimpairing the efiiciency of the procedure.

The following example is furnished by way of illustrating a procedure ofpreparing a spray metal coated article in accordance with the inventionhaving a metal surfaced base of substantially cylindrical shape androtating the same in a lathe:

Example III steel shaft of S. A. E. 1045 steel which is to be coated bymetal spraying on a section of its length is mounted in a lathe, betweenlathe centers. One lead from the source of electrical energy isconnected to the tailstock of the lathe. The other lead from the sourceof electrical energy is connected to a nickel wire of approximately /8"diameter. The shaft is rotated in the lathe at a speed of approximately600 revolutions per minute, and while the shaft is rotating, the nickelwire is first contacted with the surface of the shaft to be conditionedand as soon as the metal electrode starts to melt, the surface of theshaft, while still rotating, is lightly and repetitiously stroked withthe nickel wire over successive areas of the same, whereby the end ofthe nickel wire is caused to make and break contact repetitiously withsuccessive portions of the surface. After the desired surface area hasbeen substantially covered by relatively closely spaced amounts ofdeposited nickel from the nickel wire electrode, the treatment isdiscontinued and the surface is now ready to be sprayed upon.

Within the broad scope of my invention, the

intermediate metal, i. e., the metal intermediate the metal surface ofthe base and-the spray metal layer, essentially functions as a linkingagent and thus, firmly bonds the spray metal to the surface of the base.This function of the intermediate metal is due on the one hand to itsfusion-deposition resulting in its firm bonding to the base, and on theother hand is due to the presence of its peculiarly characteristicsurface capable of firm interlock with the particles of spray metal andformed by its freezing from semi-liquid state with the multitude ofcraters and projections of the type and character referred to. Theapplied spray metal'firmly interlocks with at least the majority ofthese projections and craters.

The herein shown photomicrographs furnished by way of illustration andnot of limitation, demonstrate the type of surface obtained byfusion-deposition of metal on a metal surface lighted in the foregroundof the photomlcrograph is one of the larger projections which, beingcloser to the camera, is somewhat out of focus.

Photomicrograph No. 2 illustrates a crosssection of the specimen used inthe preparation of photomicrograph No. 1 representing a viewperpendicular to the prepared surface at the edge of the specimen usinga conventional picral etch and max magnification. The overhangingprojections and craters with the overhanging edges and projections inthe top layer of the electrode deposited metal are clearly shown. In thelower portion of the photomicrograph is the normal structure of thesteel plate serving as a base;

- combined by fusion to this base is the electrode A one-inch depositednickel, having the appearance of solidified or frozen froth, foam orlava showing the projections and the many holes and pores, which at theupper surface of the nickel layer,

spraying steel on a sample obtained by depositing nickel on a steel baseby theelectrode deposition method referred to. The cut was treated inthe conventional manner with a picral etch. The photomicrographrepresents a 100K m 11x5.

tion. The lower portion of the photomicrogrph shows the normal structureof the d'steel base used. Bonded to this by fusion is the in-=termediate fusion-deposited nickel layer of a characteristic frozenfroth, foam or lava apmaronce. The top surface is that of thesuperimposed spray steel. The characteristic craters, projections andoverhanging edges of the inter-= mediate fusion-deposited nickel layerare clearly shown in typical interlock with particles of the spray metallayer.

its afore pointed out, any common metal may be used intermediatepractically any base and any spray metal. Thus, for instance, silver,monel, aluminum, brass, stainless steel, inconel or the like may be usedeither as fusion-dc posited metal or as base upon which the same isdeposited. In most cases, however, I prefer for best results, nickel,bronze or silver as the in= termediate metals and among these nickel asthe most satisfactory material.

When using in the above'described procedure, wire electrodes for thedeposition by fusion of intermediate metal, it is of advantage to usewires, whether round or flat shaped, having a maximum cross-sectionalwidth substantially between 6" and is". The source of electrical energymay be one providing either an alternating or a direct current. If, theprocess, herein recited by way of ex ample for the making of my novelspray metal coated articles,'is applied using large amounts of currentsubstantially continuously on a small piece of base metal, the base mayheat up con= cider-ably. This may be controlled, however, by not usingtoo much current on small base pieces or by allowing time to elapsebetween the application of the amounts of electrode material to thebase, and also by applying cooling means, such as a blast of air to coolthe surface either during or between application'of electrode material.The products in accordance with my invention include those having ametal surface or base consisting of spray metal. when sg of a metalsurface or metal base, therefore, I mean to include thereby a spraymetal surface or base.

The principal linking or bonding characteristics of the intermediatemetal with respect to the base surface are induced, as herein abovestated, by fusion-deposition. Such fusion-depositlon,'within the spiritand scope of my invention, does not necessarily connote solely fusion ordeposition by fusion to the point of complete fusion of the-entiredeposited metal, but also embraces deposition of metal only part ofwhich is fused and still further includes'the case in which the fusionof part or all of the depoflted metal, as is well understood, does notnecesproceed to the point of free-flowing liauidity.

in the preparation of spray metal coated articles in accordance withthis invention, the spray metal coating is applied in any desiredconventional manner. applied by passinga conventional metal spray gunforth and back over the intermediate fusion deposited metal layer untila spray metal coating of the desired thickness is formed.

The foregoing specific description is for purposes of illustration andnot limitation and it is therefore my intention that the invention belim-= ited only by the appended claims or their'equivalents wherein Ihave endeavored to claim broadly all inherent novelty.

I claim:

1. A spray metal coated, metal-surfaced arjections with over-hangingedges and minute craters with over-hanging edges, at least the ma=jority of said projections and craters being in interlock with spraymetal particles of said layer of spray metal, and at least the majorityof said projections being in size and spacing substantially of the sameorder of magnitude as the size of spray metal particles in the spraymetal layer.

2. A spray metal coated, metal-surfaced article in accordance with claim1 in which'said intermediate metal is nickel.

3. A spray metal coated, metal-surfaced article in accordance witticlaim 1 in which said intermediate metal is bronze.

v i. A spray metal coated, metal-surfaced ar= ticle in accordance withclaim 1 in which said intermediate metal is silver.

5. A spray metal coated, metal-surfaced article which comprises anarticle having a metal surface, a layer of spray metal, and,intermediate said metal surface and said layer of spray metal,

, fused metal deposited upon and integrally bonded to said surface byfusionto said surface and characterized by an irregular surface frozenfrom 1 -liquid state with a multiple number of first projections, amultitude of second projections with over-hanging edges and a multitudeof minute craters having overhanging edges at leastsome of said secondprojections being in size and spacing substantially of the same order ofmagnitude as the size of spraymetal particles in the spray metal layerand at least some of said first projections being of a higher order ofmagnitude, at least the majority of said second Thus the same may be

